I wonder if that's just a piece of rubble that may have been attached to the byssal threads - and it's just let go of it now that it's attached to something "better" (your rock). Otherwise, if that's a part of the clam itself, I too have no idea what it is...

Hmmm, good point. That might be exactly what it is. Thanks.

Good one Tony, looking at the pic it certainly fits! :biggrin: